There is known a drive of a nuclear reactor's control element (cf. U.S. Pat. No. 3,714,479, Cl. 310-80), comprising a screw-roller nut pair. The nut is rotated by an airtight electromotor whose rotor is installed in bearings floating in the axial direction. The axis of rotation of the nut's rollers, which are arranged in the lower part of the rotor, is parallel to the axis of displacement of the drive screw coupled to the control element. If the control element or the drive screw gets jammed, the rotor is driven vertically by the axial force until the braking lugs are matched with respective grooves provided in the motor's housing. As a result, the rotation of the braked rotor and, consequently, of the nut is discontinued, whereby an increase in the axial load upon the control element is avoided.
The design of the drive under review is such that it takes much time to drop the control element by an emergency protection signal. This is due to the fact that the nut's rollers are always engaged with the drive screw. In addition, the floating bearings make the drive's kinematics too complicated and reduce its overall reliability.
The foregoing disadvantages are partially eliminated in a drive of a nuclear reactor's control element (cf. U.S. Pat. No. 3,599,498, Cl. 74-25), comprising an electromotor and a special electromagnet with swinging armatures and rollers. The armatures are spring-loaded and spaced around a hollow shaft which is an extension of the rotor. By an emergency protection signal, the electromagnet is de-energized and the rollers are disengaged from the drive screw.
In the drive under review, the electromagnet's armatures are mounted on horizontal pivot axles and thus spaced around the hollow shaft; this accounts for an increased size of the drive. The use of the special electromagnet accounts for a great amount of metal put into the manufacture of the drive, as well as for a complicated power supply circuit.
The above disadvantages are eliminated in a drive of a nuclear reactor's control element, comprising an electromotor with a stator and a separable rotor having double-arm rocking levers and rollers that make up a detachable roller nut interacting with a drive screw under the action of the stator's electromagnetic field (cf. The Shippingport Pressurized Water Reactor, Addison-Wesley Publishing Company, Inc., Reading, Mass., USA, 1958).
In this drive, the electromotor's rotor is made separable across the diameter, and is composed of two double-arm rocking levers mounted on horizontally extending axles. The first arms of the levers make up the rotor, as such; each of the levers' second arms carries two rollers of a detachable nut. In the working position, the axis of rotation of the detachable nut's rollers is at an angle to the axis of the drive screw, which is equal to the helix angle of the drive screw. When the electromotor is deenergized, the first arms of the rocking levers, which make up the rotor, are brought together and rotated about their horizontal axles through an angle at which the rollers, mounted on the second arms, are disengaged from the drive screw. As a result, the control element, which is coupled to the drive screw, is introduced under gravity into the reactor's core. When the electromotor is energized, the first arms of the rocking levers, which make up the rotor, are brought apart by electromagnetic forces, whereupon the rollers of the nut engage with the drive screw and set it into forward motion.
Making the rotor of the drive under review separable across the diameter necessitates an increase in the internal diameter at the location of the detachable roller nut, as well as an increase in the height of the drive. The fact that the rotor is separable across the diameter also affects the electromagnetic characteristics of the electromotor. An engagement between the rollers and the lugs of the drive screw reduces the starting torque of the electromotor and the operating speed of the roller nut.